Floatation apparatus and recovery and utilization of wood fines from mill wastes



Feb. 6, 1968 Filed Sept. 22, 1964 N. S. LEA ETAL FLOATATION APPARATUSAND RECOVERY AND UTILIZATION OF WOOD FINES FROM MILL WASTES 3Sheets-Sheet 1 r I8 RAW MATERIAL I ALTERNATE OR LOGS OF PULP WOOD ISUPPLEMENTAL FEED-| sAwDUsT,e. 4 FROM; H '2 I KERF OF SAW AT I I ISAWMILL, OUTSIDE BARK AR lCl-HPPER FINES AND| E S K BARK I OTHERSELECTED L wAsTEs J l7 2 I l3 0 PRO E'TTSSQ CHI RI ERS ERRD DU PS T IFDR HEA I REMO/EDINPURlTIES 4 I PRIOR W W ART j CHIP SCREEN I l5FLOATATION DEVICE- ,REMOVING UNDERsIzE I REMOvAL OF BARK, ICH'PSSMALLFRAG REJECTS KNOTS DIRT COM- IMENTs OFBARK. CHIPPER FINES I I PREssIONWOOD AND IKNOTSID'RT AN D OTHER FRAGMENTS COMPRESSION W OF IMPURITIEs 2|l6 7 AccEPTsNORMAL ACCEPTS sIzE WOOD CHIPS UPGRADED GOOD WOOD FINESDEWATERINO DEvIcE- WATER REMOVING WATER FROM WOOD FINES DEWATERED WOODFINES I I T A PRODUCT- DIOESTER- figigf GOOD QUA ITY PULP PM FORSEMI-CHEMICAL FOR MAKING PAPER CHEMICAL PULPING FIGJ INVENTORS NORMAN S.LEA JAMES S. BRAWN Feb. 6, 1968 N. s. LEA ETAL 3,367,495

FLOATATION APPARATUS AND RECOVERY AND'UTILIZATION OF WOOD FINES FROMMILL WASTES Filed Sept. 22, 1964 3 Sheets-Sheet 2 i 79 a 78 3 I o I a[1L i l I 6| 1' FIGZ INVENTORS NORMAN S. LEA JAMES S BRAWN Feb..6, 1968N. s. LEA ETAL FLOATATION APPARATUS AND RECOVERY AND UTILIZATION OF WOODFINES FROM MILL WASTES Filed Sept. 22, 1964 3 Sheets-Sheet 5 INVENTORSNORMAN S. LEA

FIGB

FIGA

JAMES S. BRAWN United States Patent Office FLOATATION APPARATUS ANDRECOVERY AND UTILIZATION OF WOOD FINES FROM MILL WASTES Norman S. Leaand James'S. Brawn, Everett, Wash., as-

signors to Scott Paper Company, Philadelphia, Pa., a corporation ofPennsylvania Filed Sept. 22, 1964, Ser. No. 398,259 7 Claims. (Cl.209-163) This invention pertains to the recovery and utilization ofpulpable wood fractions from mixtures of fine particles of wood andbark. A particularly valuable application of the invention is concernedwith the recovery of relatively bark-free wood chips from chipper finesand/ or sawdust.

In the preparation of paper from wood, parts of logs with much, but notall, of the bark removed are reduced to chips of varying size inapparatus known as a chipper. Among the chips are particles of wood,dirt, bark, knots and compression wood that are very small, e.g. smallenough to pass through a A" screen. If good quality paper is desired,these should be separated by any suit able method or means from thelarger, normal-sized wood chips. Following such separation, the largerchips are subjected to any of various treatments, such as chemical orsemi-chemical pulping to convert them to wood pulp. By varioussubsequent treatments which constitute no part of the present inventionand which are wellknown to those skilled in the art, paper ismanufactured from the pulp.

The very small particles separated from the larger chips are known aschipper fines. conventionally, they are separated from the larger chipsby screening and are then burned to recover whatever heating value theymay possess. If the good wood could be recovered from the chipper finessubstantially free of the other chipper fines components, especiallybark, substantial economic benefits would result, for the potentialvalue of the paper that could be produced from the good Wood exceeds thevalue of the chipper fines as fuel.

Various obstacles have discouraged the recovery and utilization of thegood wood contained in the chipper fines. First of all, the separationof the small particles of good wood from the bark and other impuritiesin the chipper fines can be difficult and costly. Secondly, attempts atproducing wood-pulp from the chipper fines without removal of impuritieshave resulted in undesirably low grades of paper. Thirdly, it has beengenerally believed that if normal-sized chips are cooked along with verysmall chips, such as might be recovered from the chipper fines, theyield increase would not be sufiicient to justify the cost of recoveringthe good wood from the chipper fines.

Exemplary of various factors contributing to the problem of separatinggood wood from the back and other impurities in chipper fines is thereported observation that both bark and wood chips tend to float on thesurface of water. This frustrates attempts to use simple floatation orfloat-sink separation processes in which a mixture of two solidmaterials having respective specific gravities greater than and lessthan water are delivered to the surface of a body of water and are thenseparately recovered therefrom after the heavier material has sunkbeneath the surface. Of course, it has been observed that if chips ofcertain kinds of Wood and bark are delivered to the surface of water andallowed to stand long enough, the wood will become water-logged and sinkbefore the bark does. However, the period of time required for the woodto absorb the necessary amount of water by normal capillary actionunduly protracts the treatment and renders rapid separation impossible.Recently, it has been proposed that special float-sink separationprocedures involving vacuum and heat treatments and specializedfloatation Patented Feb. 6, 1968 media be used to hasten the separationof mixtures of bark and wood chips. As is well known, however, theemployment of heat, vacuum and specialized media introduce additionalcomplexities and cost factors which it would be desirable to avoid, ifpossible. Consequently, there is still a need for additional methods andapparatus of a simple, economical, rapid and efficient nature forseparating good wood fragments from fragments of bark and otherimpurities.

It is the principal object of the present invention to fulfill the aboveneed. Another object is to provide methods and means for separatingchips of wood and bark by floatation without the necessity of resortingto vacuum treatment, heat treatment or specialized floatation media.Still another object is to provide methods and means whereby bark chipsmay be caused to sink and good wood chips float in water to facilitatetheir separation. A further object is to provide a consistentlyefiicient float-sink separation process for separating mixtures of verysmall good wood and bark fragments despite relatively wide and frequentvariations in the ratio of bark to good wood in said mixtures. Anotherobject is to provide methods and means for upgrading, e.g. lowering thepercentage of various impurities, such as bark, knots and compressionwood, in particulate mixtures of wood and one or more of theseimpurities, the mixtures being characterized by particles which willpass through a screen with A" openings. Still another object is toprovide an integrated process for recovering pulpable wood from chipperfines and for converting the recovered wood to pulp. Another object isto provide a process for recovering good wood from chipper fines and forconverting said chipper fines to pulp in the presence of one or moreadditional woody materials. Still other objects and advantages of theinvention will suggest themselves to persons skilled in the art uponconsideration of the explanations which follow.

According to the present invention, it has been found that chipperfines, sawmill sawdust and other selected wood wastes may be upgradedand converted to good pulp in the presence or absence of normal-sizewood chips, e.g. those which will be retained on a screen with A" toopenings. Thus, material whose value has been largely wasted by burningit as fuel may now be more beneficially utilized by converting it topulp which displays good strength properties and is readily bleached.

According to the present invention, mixtures of fine particles of wastewood and impurities, e. g. particles small enough to pass through ascreen with openings of approximately 4, are submerged in an aqueousbath; a generally downwardly directed force is applied to the mixture inthe bath for forcibly conducting the mixture downwards in the bath; themixture is then released from the downwardly directed force. Uponcompletion of the above operations, the good wood has a tendency to risein the bath while the impurities sink or at least remain an appreciabledistance below the surface. It has been found that the performance ofthe above operations will cause a predominant proportion of the goodwood in the mixture to rise to the surface while a predominantproportion of the impurity or impurities fails to so rise. Consequently,the invention facilitates the recovery from the surface of the bath ofgood wood freed of a substantial proportion of the impurity orimpurities in the original mixture.

Preferred embodiments of the various methods and apparatus of thepresent invention will now be described in connection with theaccompanying drawings, wherein:

FIGURE 1 is a schematic diagram of certain methods constituting a partof the invention;

FIGURE 2 is a vertical sectional view of floatation apparatusconstructed in accordance with the invention, taken along section line22 of FIGURE 3;

FIGURE 3 is an end view of the aforesaid floatation apparatus; and

FIGURE 4 is a partially broken out sectional view taken along sectionline 4-4 of FIGURE 2.

In a preferred embodiment of a method according to the invention, asshown in FIGURE 1, logs of pulp wood are passed through a barker 11 forremoval of as much bark 12 as is practicable. The debarked logs are thenprocessed in a chipper 13 wherein the logs are reduced to an assortmentof chips of good wood, bark, knots, dirt, compression wood and otherimpurities. In accordance with conventional practice, the chips areseparated into normal size and undersize chips. The usual method ofseparation is by means of a chipper screen 14. Usually the chipperscreen has openings of about 41" or and the rejects 15, the materialwhich passes through the screen, is referred to as chipper fines and ischaracterized substantially, if not completely, by fragments which willpass through a A" screen. The accepts 16, of course, are the larger,normal size chips which do not pass through the screen.

In accordance with prior art practice, the chipper fines are sent to theboiler house 17 where they are burned to recover whatever heat valuethey may contain. Contrary to prior art practice, the present inventioninvolves subjecting chipper fines, or other fine wastes 18, or mixturesthereof to a treatment to separate various impurities therefrom, such asbark, knots, dirt, compression wood and other impurities.

The preferred, but not necessarily the only, method of separation is byfloatation according to a new process and in a novel floatation device19, which constitutes part of the present invention. The floatationdevice upgrades the chipper fines by separating them into rejects 20,constituting the bulk of the impurities originally present, and intoaccepts 21, constituting a substantial portion of the good woodoriginally present in the chipper fines. Water 23 is removed from theaccepts 21 in any suitable dewatering device 22, while the rejects aresent to boiler house 17. The invention provides two alternate orcomplementary modes of dealing with the dewatered accepts or wood fines24.

According to one mode of treatment, constituting the preferred mode, thedewatered wood fines 24 are combined or mixed with the accepts 16. Thenthe mixture of the small and large chips is converted to pulp 28 by anysuitable method or means 27, such as by mechanical, semichemical orchemical pulping. It has been found that this mode of operation canincrease production rates in chemical pulping processes, for theupgraded wood fines when added to normal chips in a ratio of up to about1:10, tend to fill in the voids between the normal-sized chips, thusincreasing the weight of material that can be placed in a digester of agiven volume, with proportional increases in the amount of pulp producedper cook. Any chemical pulping technique or type of cooking liquor maybe employed, e.g. soda, acid sulfite, kraft, NSSC and so forth. Theweight ratio of active chemical(s) to wood (bone dry basis) charged tothe digester may correspond with or differ from the ratiosconventionally used in present day commercial operations for a givenliquor or technique. However, the use of conventional ratios ispreferred, thus necessitating slight but non-injurious simultaneousincreases in the concentration of active chemicals in the liquor anddecreases in liquor volume.

According to the second mode of treatment for the dewatered wood fines24, the fines are placed in a digester 29 for conversion to pulp 28. Thebest method of conversion for this material appears to be acid sulfitepulping, employing conventional liquors, temperatures, pressures,concentrations and liquor to wood weight ratios. To facilitatecirculation in downflow forced circulation digesters, it is recommendedthat the bottom strainer be covered with a layer of normal size chips toinsure that the wood fines do not interfere with circulation. Otherwise,the cooking procedure and conditions are conventional.

A preferred embodiment of the floatation apparatus of the presentinvention is illustrated in FIGURES 2, 3 and 4. In accordance with theinvention, a floatation tank 30 is provided, having a closed bottom 31and side and end walls 32, 33, 34 and 35, respectively. Any of theaforesaid walls, in this case end wall 34, has a lip 36 which issituated below the upper edges of the adjoining wall portions. Theelevation of the lip determines the intended level 42 of the surface ofan aqueous floatation bath 43 which is to be maintained in the tank.Extending downwardly and laterally from the lip 36 and end wall 34 is aspillway 37.

The floatation apparatus of the invention may include a headbox orsluice box. The sluice box or headbox may be located within or withoutthe tank 30 proper, and the walls of the headbox may be separate fromand/or part of the walls of the tank. In the present embodiment, therear and side walls of the headbox or sluice box are part of therespective upper portions of the rear and side walls 35, 32 and 33 oftank 30. The front wall of the headbox in the present embodiment is agenerally vertical bafiie 44 extending transversely of the tank fromside wall 32 to side wall 33 and between end walls 34 and 35. The baffle44 has an upper edge 45 disposed above the intended level 42 of thefloatation bath, side edges 46 and 47 joined to side walls 32 and 33respectively, and a bottom edge 48 disposed below the intended level ofthe floatation bath. Thus, the baffle divides the headbox and tank intoseparate chambers at the level of the lip 36 and for an appreciabledistance below said level, but does not close off communication betweenlower portions of the headbox and tank. It is apparent therefore, thatthe baffle will effectively divide the surface and upper portion of thefloatation bath into separate portions, while permitting communicationbetween that portion of the bath 43 contained in the lower portion ofthe headbox and that bath 43 contained in the tank 30 proper.

In accordance with the present embodiment, the bottom wall of theheadbox is a generally horizontal baffle 39 extending transversely ofthe tank 30 along end wall 35 from side wall 32 to side wall 33. Battle39 extends longitudinally from end wall 35 to a position beneath andvertically spaced from the bottom edge 48 of bafile 44. It may, ifdesired, extend a short distance further into the tank 30. It should beobserved that the bottom edge 48 of vertical baffle 44 and the adjoiningportion of generally horizontal bafiie 39, as well as the adjoiningportions of tank side walls 32 and 33, form a generally horizontalpassageway 40 between the headbox and the tank, which passageway iswholly situated at an appreciable distance below the level of lip 36 andis therefore similarly below the intended level 42 of the surface of thefloatation bath to be maintained in tank 30. This passageway providescommunication between the headbox beneath the intended level of thefloatation medium.

The headbox 38 is provided with a means for delivering chips thereto,such as a chute 49 and star feeder 41. Other means, such as conveyors,open chutes and conduits of various types may also be employedsupplementary to or in substitution for the chute 49 for evenlydistributing feed material in the headbox at a controlled rate. Also,although the chute 49 is positioned to deliver the chips to the surfaceof the floatation bath, the chips may also be delivered to the headboxbelow the surface of the bath.

Associated with the headbox are means for inducing therein a downwardlydirected flow of floatation medium and chips. The preferred means is aconduit and pumping system which will now be described. In the presentembodiment, there is an outlet in tank 30 well below the surface of thebath at a location widely separated from the headbox. Outlet 60 isconnected to the input side of a pump 64 via conduits 61, 62 and 63. Thedischarge side of pump 64 is connected with a spray header conduit 50via conduits 65, 66 and 67. Conduit 50 extends transversely of thefloatation device above the intended bath level 42. It has a pluralityof transversely spaced branch conduits 59 extending into chute 49 andhaving outlets directed downwardly towards the intended level of thebath at a plurality of transversely spaced points. The concluit systemand pump described above are adapted to direct a plurality of forcefuldownward sprays of floatation liquid against the surface of thefloatation bath in the headbox at a plurality of transversely spacedpoints.

The downwardly directed flow of floatation medium and chips may beinduced in a number of ways. For instance, the action of the sprays maybe supplemented by downwardly directed mechanical agitation of thefloatation medium in the headbox, or mechanical agitation may besubstituted entirely for the action of the sprays. Vigorously pumpingthe floatation medium and chips out of the headbox may also be used tosupplement or replace any of the modes mentioned above for inducing therequisite flow. It will be apparent therefore to persons skilled in theart that a wide variety of means may be employed for inducing thedesired flow.

Any convenient means may be employed to introduce additional liquid totank 30 to make up for that lost by overflow over the lip 36. Accordingto the present embo'diment of the invention a make-up liquid supplyconduit 75 provided with a valve 76 opens into the tank 30 through endwall 35.

Means may be provided for removing accumulations of material from thelower portion of tank 30. In the present embodiment, the means include atransversely extending channel 68 fitted to the bottom 31 of the tank. Aconveyor 69 extends through channel 68, through first vertical conveyorguide means 70, through upper horizontal conveyor guide means 71,through a second vertical conveyor guide means 72, and back into channel68. The vertical guide means 70 and 72 are fully enclosed, aresubstantially leakproof and are joined by liquid-tight connections totank walls 33 and 32 respectively. The conveyor discharge port 73 anddriving means 74 are located above lip 36 and therefore are also abovethe intended surface level of the floatation bath in tank 30 and in thevertical conveyor guides.

Any suitable means for removing accumulations from the bottom 31 of thetank 30 may be employed. The means described above are preferred becausethey prevent any substantial flow of floatation medium out of the bottomof the tank, because they are eificient and because they may operate ona continuous basis. The use of means which operate intermittently ormanual clean-out are possible, but automatic continuously operatingmeans are considered best for high volume commercial operations.

The preferred embodiment of the present invention includes certainfeatures which, though not deemed essential to the broadest concepts ofthe invention, nevertheless render the present embodiment unusuallyeflicient. For instance, it has been found desirable that the baflle 39incline upward from its point of attachment to end wall 35 and extend ashort distance, e.g. l or 2 inches, beyond baflle 44. Also, it has beenfound that the best yields are obtained when the depth of the baffle 44beneath the surface of bath 43 is about 4 m6 inches, although otherdepths have been employed. Further, it has been found desirable toprovide a plurality of vertical flow regulation baffles 77, 78 and 79 intank 30, extending from side wall 32 to side wall 33 between end walls34 and 35. The bafiles should have their upper edges positioned a shortdistance, e.g. about an inch, below the intended level 42 of the surfaceof the floatation bath and their bottom edges should be spaced from thebottom and end wall 34 of the tank. Furthermore, it has been found thatthe convergence of the end walls 34 and 35 towards the bottom of thetank reduces the area from'which accumulations of sunken material mustbe removed, thus facilitating the removal operations. Still another ofthe advantageous features of the present embodiment is the placement ofthe headbox 38 and the lip 36 at opposite ends of the tank 30, so thatthere will be a relatively straight-line flow of floatation liquid andfloated material from one end of the tank to the other. Moreover, thevertical distance between bafiles 44 and 39 should be relatively short,e.g. 3" to 5", if the best effect is to be obtained from the baflle 39in turning the flow of floatation liquid and chips from a downward flowto a generally horizontal flow as it departs from the headbox. Finally,although embodiments of the invention have been constructed in whichthere is no horizontal baflie, and such embodiments have been able tomake a worthwhile separation, a horizontal baffle is of considerablebenefit, and its use is therefore recommended.

The operation of the floatation device of the present invention isrelatively straight-forward. Water is customarily employed as thefloatation medium, although other floatation media known to personsskilled in the art may also be used. The use of fine particles of anyspecies of wood suitable for commercial processes of making paper iscontemplated. Generally speaking, the feed material will contain notonly fragments of good wood, but also the various impurities previouslymentioned. The fragments may vary widely in size and shape, but the feedmaterial will be characterized by a substan-' tial proportion offragments which will pass through a quarter inch screen. Such fragmentsare available not only in the form of chipper fines, but also in theform of sawmill kerf sawdust and other selected mill wastes.

The feed material 56 is delivered to the headbox 38 through chute 49,which drops the feed on the surface of the floatation bath adjacent thesprays 51. The sprays beat downwardly upon the fragments and submergethem. The generally downward flow in the headbox induced by the sprays51 conducts the fragments downward in the headbox. The flow of liquidand fragments generally follows the direction indicated by the arrows inFIGURE 2. The flow passes under the baffle and out into tank 30, whereit is released from the downwardly directed force produced by the sprays51. Then, a portion of the fragments 57, which is mostly good wood,rises to the surface and flows out of tank 30 over lip 36 and throughchute 37, as indicated by the arrows in FIGURE 3. The good wood exitingtank 30 via chute 37 is recovered by any suitable means forming no partof the present invention. Another portion 58 of the fragments of feedmaterial, containing mostly one or more of the impurities, such as bark,dirt, compression wood and knots, sinks to the bottom of tank 30. Theimpurities pile up in the bottom of the tank 30 and are graduallywithdrawn therefrom through channel 68.

The rate of flow of floatation medium from conduit 50 should besuflicient to maintain a positive flow of floatation medium from theheadbox to the tank 30 and over the lip. Generally, increased velocityof flow is associated with increased yields and a somewhat increasedcontent of sapwood in the accepts, since sapwood sinks quite slowly. Thepercent of bark in the accepts, however, remains reasonably stable overa relatively wide range of velocities'Temperature does'not appear to bea critical feature, and the process will ordinarily be carried out atambient temperatures, e.g. about O-40 C. and at the prevailingatmospheric pressure. The floatation medium must, of course, have aspecific gravity inter.- mediate between the desired and undesiredcomponents of the feed material. The rate of introduction of feedmaterial to headbox should be such as to keep in step with the rate ofdisappearance of feed material from the headbox. The latter rate, ofcourse, is dependent upon the flow rate and pressure of the floatationmedium issuing from conduit 50. Generally speaking, the higher thepressure, the better.

The following examples illustrate, but are not intended to limit theinvention. All parts are by weight unless the contrary is indicated.

Example 1 Hemlock, white fir and lodgepole pine, in a weight ratio (bonedry basis) of 60 parts to 28 parts to 12 parts, is debarked, reduced tochips and sized with a chip screen having A openings to produce A1"accepts and %i" chipper fines or rejects. The chipper fines constituteapproximately 2.7% of the weight of the chips fed to the chip screen.The moisture content of the chipper fines varies from about 47 to 62%and averages about 53%. The bark content averages about 0.62%.

The above-described chipper fines are processed in a floatation unitconstructed in accordance with the invention. The unit is 24" wide, 4deep and 8' long. The floatation tank or cell is divided into tworetention chambers of approximately equal volume, as previouslydescribed. The floatation bath is water, which is maintained at a depthof about 3 in the retention chambers. The baflle between the headbox andfloatation tank proper extends vertically about 5" beneath the surfaceof the floatation bath. The rate of feed of chipper fines is about 12B.D. pounds per minute and water is sprayed into the headbox at a ratethat varies from 75120 g.p.m. and is usually about 75-100 g.p.m.

The accepted material which floats on the surface of the bath, has anaverage moisture content of about 66% and an average bark content ofabout 0.17%. The rejects have a moisture content of about 63%. Theyield, pounds of B.D. (bone dry) accepts divided by the sum of poundsB.D. accepts plus pounds B.D. rejects, is 63.81%.

Example 2 The procedure of Example 1 is repeated, substituting s'awmillkerf sawdust and blends of chipper fines and sawmill kerf sawdust forthe chipper fines. Similarly, successful results are obtained.

Example 3 The procedure of Example 1 is repeated, except that thevertical underwater extension of the baffle between the headbox andfloatation tank proper is varied from 4" to 6". The system continues tooperate successfully.

Example 4 Accepted material produced in Example 1 is given a sulphitedigester treatment utilizing ammonia base acid. 4.54 kg. of 47.2% B.D.hemlock chips are placed over the bottom strainer in a downflow forcedcirculation digester. 120.86 kg. of the accepted material produced inExample 1, 32.25% B.D. are charged to the digester over the hemlockchips, thus making a total charge of 41.31 B.D. kg. 215 liters ofammonia base cooking acid having a tot-a1 S content of 7.80% and acombined S0 content of 0.85% are employed in an approximate acid to woodratio of 5.1: 1 for cooking the digester charge in accordance with thefollowing schedule and conditions:

COOKING DATA Time (Hrs: pH Total Comb. Temp., 0.

Min.) S0 802 Front Center Back The cooking proceeds without any unusualproblems. Bleachability of the product is about 6.10% C1 No. The

yield is 44.88% B.D. yield. The percent screenings is about 0.32%, whichis much lower than the normal amount of screenings obtained from regularchips. When TAPPI handsheets of the pulp produced in accordance withthis example are prepared with similar handsheets of unbleachedAnacortes Alder, and are tested for Mullen, Tensile, Tear, SpecificVolume and Freeness at beating times of 0, 10 and 30 minutes, thefollowing results are obtained:

As can be seen from the above data, paper produced from upgraded chipperfines in accordance with the present invention compares favorably withthat prepared from unbleached alder.

Example 5 Approximately two B.D. tons of the material recovered inaccordance with Example 1 are thoroughly mixed with tons of 47% B.D., A"chips accepted by the chipper screen of Example 1. The upgraded chipperfines constitute approximately 5% by weight of the resultant mixture.The mixture is placed in a forced circulation plant digester and iscooked while approximately 38,800 gallons of acid sulfite cooking liquorare circulated. The cooking liquor is similar to that employed inexample 4 and differs from conventional acid sulfite cooking liquorsused for cooking normal-size chips only in that suitable adjustmentshave been made in the acid strength, both free and combined, to accountfor the presence of the chips, as explained below.

The mixture of 5% upgraded chipper fines and 75 (wet) tons of normalchips has essentially the same apparent volume as the 75 (wet) tons ofnormal chips would have alone. However, the B.D. weight and real volumeof the mixture are greater than that of the normal chips alone. Thetotal weight of wood is 5% greater. An upward adjustment of 5% in thepercentage of free and combined S0 is needed to pompensate for theweight increase. However, the increased real volume of charge materialdecreases the number of gallons of cooking acid that can occupy thedigester. The two tons of chipper fines occupy approximately 540 ft. ofwhich 30% or 162 ft. is real volume. A loss of 162 ft. of digeste-rspace which would otherwise be available for cooking liquor involves areduction of 1,200 gallons from the normal 40,000 gallons of acid or a3% reduction in the total charge of acid. Therefore, the acid strength,both free and combined is raised by 8% in order to maintain the sameacid to wood ratio as is present when QQQlfi Wit AQu fines- The cookingschedule is as follows:

COOKING SCHEDULE Time (Hrs.:Min.) Circulation, Temperature, Pressure,

g.p.m. C. p.s.i.g

: 3, 550 104 100 I 3, 500 115 100 1 3, 200 122 100 2, 450 127 100 1 1,900 131 100 I 1, 600 134 100 Z 1, 500 135 100 I 133 100 1 133 93 :30 12865 A control cook with 75 tons (wet) of the chips alone, but without the8% boost in concentration of the cooking liquor was carried out in asimilar manner. The cooking schedule was as follows:

COOKING SCHEDULE In comparing the results of the two cooks describedabove, it is noted that circulation falls off sooner with the mixture ofupgraded chipper fines and normal chips. Therefore, the control cookcontains slightly fewer screenings. However, the cook with the upgradedchipper fines produces a pulp of normal chlorine number, dirt count andstrength properties, and a higher yield of useable pulp. Therefore, itappears that advantageous results are obtained by admixing normal sizechips with wood waste from which the impurities have largely beenremoved and by chemically digesting the resultant mixture.

What is claimed is:

1. Separatory apparatus of the flotation type, comprising: a tank,including a bottom, first and second end Walls, and a pair of sidewalls, said walls having upper edges and being joined to said bottom andto one another so as to contain a flotation medium; the first of saidend walls having an overflow lip situated beneath the level of the upperedges of the remaining wall means whereby said lip maintains saidflotation medium in said tank at a predetermined level; a generallyvertical baffle member extending between said side walls at and for anappreciable distance below said predetermined level; a generallyhorizontal batfle member secured to the second of said end walls andextending from one of said side walls toward the other side wall andextending beneath said generally vertical baffle in vertically spacedrelationship therewith; said baflie members, said second end wall andsaid side walls defining a sluice box, and said baflie members and saidside walls defining a generally horizontal passage between the sluicebox and tank proper; a plurality of spray means directed downwardly intosaid headbox from above said predetermined level at a plurality oftransversely spaced points; an outlet in said tank at a location remotefrom said sluice box for the withdrawal of flotation medium therefrom;and means for recirculating said withdrawn flotation medium to saidspray means under pressure; means in the bottom of said tank for theremoval of accumulated solids therefrom; and means for supplyingparticulate material to the sluice box.

2. Apparatus in accordance with claim 1 wherein said tank is providedwith means for the introduction of makeup flotation medium to replacethat which is lost by overflow over said overflow lip.

3. Apparatus in accordance with claim 1 wherein said horizontal bafflemember is inclined slightly upwardly as it extends away from said secondend wall, and extends a short distance beyond said vertical bafiiemember.

4. Apparatus in accordance with claim 1 wherein said end walls inclineinwardly towards the tank bottom.

5. Apparatus in accordance with claim 1 wherein generally vertical flowregulation baffle means are provided in the tank proper, said bafflemeans extending transversely in said tank from one of said side walls tothe other of said side walls and having upper edge means situated ashort distance below the aforementioned predetermined level, and bottomedge means slightly spaced upwardly from the bottom of said tank.

6. Apparatus for separating wood fines of differing densities comprisinga sluice box having an upwardly inclined bottom wall, said sluice boxdefining an exit port proximate the upper end of said bottom wall, achamber communicating with said port and having Walls above the level ofsaid port in said sluice box and adapted to contain a body of waterextending above said port, channel means located proximate said sluicebox and in fluid communication therewith to introduce wood finestherein, and conduit means in fluid communication with said sluice boxto introduce substantially vertically downwardly into said sluice box anaqueous medium whereby fines entrained in such downwardly introducedaqueous medium are uniformly distributed through said sluice box exitport upwardly toward the surface of the fluid located in said chamberwhereby fines of different densities readily separate in said fluid andare separately recoverable.

7. Apparatus as set forth in claim 6 including at least one verticallydisposed baflie spaced from said sluice box and having a top facelocated above said exit port of said sluice box and below the top of thewalls of said chamber and a bottom face located above the bottom of saidchamber.

References Cited UNITED STATES PATENTS 450,063 4/1891 Fitch 209-1,056,952 3/1913 Smith 209-162 1,937,190 11/1933 Chance 209-1732,764,289 9/1956 Scheid 209173 3,042,198 7/1962 Slavich 20944 S. LEONBASHORE, Primary Examiner.

6. APPARATUS FOR SEPARATING WOOD FINES OF DIFFERING DENSITIES COMPRISINGA SLUICE BOX HAVING AN UPWARDLY INCLINED BOTTOM WALL, SAID SLICE BOXDEFINING AN EXIT PORT PROXIMATE THE UPPER END OF SAID BOTTOM WALL, ACHAMBER COMMUNICATING WITH SAID PORT AND HAVING WALLS ABOVE THE LEVEL OFSAID PORT IN SAID SLUICE BOX AND ADAPTED TO CONTAIN A BODY OF WATEREXTENDING ABOVE SAID PORT, CHANNEL MEANS LOCATED PROXIMATE SAID SLUICEBOX AND IN FLUID COMMUNICATION THEREWITH TO INTRODUCE WOOD FINESTHEREIN, AND CONDUIT MEANS IN FLUID COMMUNICATION WITH SAID SLUICE BOXTO INTRODUCE SUBSTANTIALLY VERTICALLY DOWNWARDLY INTO SAID SLUICE BOX ANAQUEOUS MEDIUM WHEREBY FINES ENTRAINED IN SUCH DOWNWARDLY INTRODUCEDAQUEOUS MEDIUM ARE UNIFORMLY DISTRIBUTED THROUGH SAID SLUICE BOX EXITPORT UPWARDLY TOWARD THE SURFACE OF THE FLUID LOCATED IN SAID CHAMBERWHEREBY FINES OF DIFFERENT DENSITIES READILY SEPARATE IN SAID FLUID ANDARE SEPARATELY RECOVERABLE.